The present invention relates to direct current electric motors and in particular to rotors for direct current electric motors.
Mechanical linkage and hydraulic pressure operated controls for vehicles are well known in the art, and generally comprise control input devices operated by a user such as steering wheels, shift levers, and foot pedals which are directly interlinked with various vehicle controls individually or by combinations of mechanical push rods, gears, cables, or hydraulic pressure lines. Such controls have been utilized in vehicles such as automobiles and trucks since the inception and initial manufacture of such vehicles. As technology has advanced, today""s vehicles regularly incorporate computers in various forms to assist in vehicle control. These computers can rapidly acquire various objective input data, analyze the data, and adjust the vehicle controls based on the data analysis to more readily optimize the operation of various vehicle systems and controls. As a result of the rapid computational power of the computers the computers can issue control commands at a much faster rate than older technology mechanical system configurations can respond. The requirement for increased control response times were initially felt in the aerospace industry where modern aircraft have evolved from the use of mechanically linked controls to electrically operated controls in a concept commonly known as xe2x80x9cfly-by-wirexe2x80x9d.
Other industries such as the auto industry are now also in need of such rapid response capability in the control systems of such vehicles. One such system desired to be adaptable to electrically operated controls on many automobiles requiring rapid control response are anti-lock brake systems (xe2x80x9cABSxe2x80x9d). The concept of an ABS on vehicles is to permit the user to apply a constant pressure to the brake pedal which the braking system senses whether or not the wheels are in a skid to provide maximum braking force to the wheels while the wheels are turning and to release the braking force when a skid is sensed. Such cycling between different braking states occurs rapidly to minimize the braking distance of the vehicle while preventing the vehicle wheels from locking in a skid. To provide the desired and optimum actuation of this type of system requires new modes of system actuation other than prior art mechanical means. Electric servos and DC electric motors with improved response times readily lend themselves to integration with the onboard computers and vehicle systems.
Some controls such as those used with the above-mentioned ABS require rapid cycling of the servos or motors wherein the desired cycling times are in the range of milliseconds. The cycling rates of these control motors are a function of a number of factors, one of which is motor size. Larger motors generally require more time in which to cycle since the moving parts of the motor are generally of a greater mass and correspondingly have a larger inertia which must be overcome to either start or to reverse direction. Because of the torque and power requirements to provide sufficient control forces such as those required on vehicle brakes, current motor designs while a significant improvement over mechanical linkage, still do not optimally lend themselves to applications wherein there is also a requirement for rapid cycling of the control motor.
Prior art motor designs typically include a stator comprising a series of electrical windings to generate magnetic fields that in turn induce the rotation of a rotor. The rotor is generally of a relatively high mass wherein the rotors generally comprise a shaft upon which is mounted a high-density magnetic core with a plurality of permanent magnets affixed about its periphery. The large mass of the rotor results in a large rotational inertia, which is then difficult to reverse or cycle at the desired high cycling rates. Thus, there is a need for a DC electric motor that is capable of delivering greater torque with reduced rotational inertia to facilitate rapid control cycling.
One aspect of the present invention is a direct current electric motor including a housing with a stator that further includes a plurality of electrically conductive windings. The stator defines a central cavity in which a rotor is rotatably mounted therein. The rotor comprises a shaft and at least two magnets affixed in a radially spaced manner from the shaft and includes a rotor core between the shaft and the magnets wherein the rotor core is rotationally de-coupled from the shaft and the magnets.
Another aspect of the present invention is a rotor for a DC motor. The rotor includes a shaft and a plurality of magnets rotationally coupled to the shaft and radially spaced there from the shaft and the magnets define a cannular cavity therebetween in which is positioned a rotor core. The rotor core is rotationally de-coupled from the shaft and the magnets.
Yet another aspect of the present invention is a direct current electric motor capable of rapid reversal rates. The motor includes a housing and a stator affixed within the housing wherein the stator defines a substantially cylindrical cavity having a central axis. A rotor is journaled to the housing for rotation about the central axis and is positioned within the cylindrical cavity. The rotor includes a shaft having an axis of rotation coincident with the central axis and a plurality of magnets radially spaced from the shaft and rotationally affixed thereto. The shaft and the plurality of magnets define a cannular cavity within which a rotor core is positioned and is rotationally de-coupled from the shaft and the magnets.
Still another aspect of the present invention is a method for minimizing the rotational inertia of an electric motor rotor. The method comprises the steps of providing a rotor shaft; mounting a plurality of magnets about the shaft in a rotationally coupled manner; and mounting a rotor core about the shaft and within the magnets in a rotationally de-coupled manner.
These and other features, advantages, and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings.